Light emitting diodes (LEDs) are assuming a more prominent role in the lighting industry. Improved consistency in the manufacture of LEDs along with improvements in the utilization of mounting structures to act as heat sinks have resulted in a light source that is economically competitive and operationally superior to the conventional incandescent and fluorescent lighting that has been the staple of the industry for several decades. As the use of LEDs has matured from their use in warning and other signals to general lighting fixtures, it has become necessary to develop optics that allow for the dispersion of the harsh, intensely concentrated beam of light emitted by the LED into a softer, more comfortable illumination that presents a uniform and even appearance.
One way of attaining a more uniform appearance is to control the light rays generated by the LEDs so as to collimate the light rays within an optic so that the light presents a uniform appearance when it exits the optic. This can be accomplished through the use of total internal reflection (TIR) in which light traveling through an optic is reflected back into the optic from a surface, provided that the incident light does not exceed a critical angle with respect to the surface. Specifically, the light rays continue to travel through the optic until such rays strike an index interface surface at a particular angle less than an angle measured with respect to a line normal to the surface point at which the light rays are incident (or, equivalently, until the light rays exceed an angle measured with respect to a line tangent to the surface point at which the light rays are incident) and the light rays escape.
Conventional lighting optics used with LEDs do not necessarily result in a uniform lighting appearance as one viewing the optic may see what appears to be numerous dots resulting from imaging of one or more LEDs of a multi-die LED package.
Some known optics use a single TIR wall. While this helps to collimate the light rays, a single wall is inherently limited in its ability to collimate light developed by the light source. The remainder of the light is refracted to obtain a desired degree of collimation, which results in a more uneven distribution of light that undesirably contributes to imaging of the LEDs.